Effects of storage on measurements of potential microbial activities in stream fine benthic organic matter

Sample storage can significantly influence measured microbial activities in stream fine benthic organic matter (FBOM), possibly confounding effects of sample variability and short-term changes in activity. Denitrification potential, acetylene reduction and respiration rates, mineralizable N and extractable ammonium concentrations, and beta-glucosidase and phosphatase enzyme activities of FBOM from first-order mountain streams in the western Oregon Cascade Mountains were assayed at various times after collection to determine potential storage effects. Denitrification potential, phosphatase activity, and extractable ammonium remained stable over a minimum of 11 h of storage at 5 degrees C. Mineralizable N concentrations, respiration rates, and beta-glucosidase activity all decreased within 12 h of collection. Results varied for acetylene reduction. Once assay conditions were established, denitrification potential and respiration rates were linear with incubation time. Based on paired t-tests, measures of acetylene reduction, denitrification potential, respiration rate, beta-glucosidase activity, and phosphatase activity were generally similar at a 1-wk interval within the same stream reaches.